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This dissertation describes modular chemical sensing systems (MCSS) and how the sampling interfaces of these systems can be regenerated. By regenerating the sampling interface, the reproducibility of the sensing system's measurements can be improved over traditional stationary sampling interfaces. The first modular chemical sensing system explored in this work is a chemiluminescent biosensor with fiber optic detection. The concept of in situ replacement the part of the sensor that imparted selectivity and pre-concentration, in this case the antibody layer, grew out of this work after conventional immobilization strategies failed and non-covalent immobilization was explored. This led to exploration of other systems or system components that can be regenerated to increase the stability of a chemical sensing system over time.These other systems include a dissolved oxygen sensing system for marine deployment, the liquid core waveguide, and supported liquid membrane sampling interfaces. The oxygen sensing system's sampling interface is an electrolyte-filled tubular membrane. The electrolyte is renewed with each measurement, thereby renewing the sampling interface of the system. Membrane biofouling is prevented by periodically illuminating the tube with UV radiation. The liquid core waveguide can be used as both a detector and sampling interface. It is a semi-permeable membrane in which the core material can be renewed with each measurement, regenerating the sampling interface. In addition, it is a long-path optical cell that can be used for sensitive absorbance-based or Raman detection. Supported liquid membranes were also explored in this work as a sampling interface for two sensing systems, the FlowProbe and the liquid core waveguide. Supported liquid membranes provide one-step extraction from a bulk matrix where the reagent acts as the sink for the extracted species. Renewing this reagent regenerates the sampling interface. Additionally, in situ replacement of the supported liquid membrane was explored.